1. Field
The present invention relates to an optical transmission apparatus, an optical interface device, and an optical transmission method.
2. Description of the Related Art
In recent years, an optical wavelength division multiplex (WDM) system is often used for an optical communication network. In the optical wavelength division multiplex system, a plurality of optical signals of different wavelengths are multiplexed and transmitted through one optical fiber cable. The optical wavelength division multiplex system includes a plurality of optical wavelength division multiplex apparatuses that are connected via an optical fiber cable.
A certain type of optical wavelength division multiplex apparatus is compatible with a pluggable type (plug-in/pullout type) optical device (hereinafter “pluggable optical device”). A pluggable optical device is a device that mainly carries out a process of converting an optical signal input from a client line into an electric signal and of converting an electric signal into an optical signal to output the optical signal to a client line. For example, an XFP (10 Gbit/s Small Form factor Pluggable) (“10 Gigabit Small Form factor Pluggable Module”, [online], [searched on Apr. 21, 2008], Internet <URL: http://www.xfpmsa.org//FPF_Rev4—5_SFF_INF—8077i.pdf>) and an SFP (Small Form Factor Pluggable) are known as pluggable optical devices. When an optical wavelength division multiplex apparatus compatible with a pluggable optical device is used, the pluggable optical device can be plugged in or pulled out on a live line even if the optical wavelength division multiplex apparatus is still in the course of startup. This allows communication businesses and network administrators to deal flexibly with a change in a transmission distance or the wavelength of an optical signal.
The above optical wavelength division multiplex apparatus, however, poses the problem that live-line plug-in of the pluggable optical device may exert a negative effect on an IC (Integrated Circuit) in the optical wavelength division multiplex apparatus. Specifically, when the pluggable optical device is plugged into the optical wavelength division multiplex apparatus by live-line plugging, a noise may be generated on a voltage applied to a CDR (Clock Data Recovery) in the optical wavelength division multiplex apparatus before the startup of the pluggable optical device. The generation of such a noise may push the applied voltage out of the range of an input rated voltage for the CDR, thus causing a concern for a negative effect on the CDR.